Compaction quality control of soil-rock filled subgrades in mountainous areas

Soil-rock mixtures with large particle size variations are often used as fill materials for expressway construction in mountainous areas. Conventional testing methods do not enable fast and nondestructive monitoring of real-time changes in the compaction quality of soil-rock filled subgrades. Selecting an appropriate evaluation method is the key to controlling the compaction quality of a soil-rock filled subgrade. In this study, three-dimensional DEM models of subgrade materials were reconstructed by a spherical harmonic series whose harmonization degree was fixed at 15. The macroscopic and mesoscopic behaviours and characteristics of the subgrade under vibratory rolling were analysed. The results showed that the porosity, contact force and coordination number of the subgrades tended to be stable in the last two passes. The subgrades with 4 filler combinations presented the similar mechanical anisotropy and meso-mechanical states. On-site monitoring of subgrades under vibratory rolling and settlement after construction was performed, and the results were considered. An evaluation method and criterion to control the compaction quality of the SRM subgrade was proposed, i.e., whether the average value of the vibration compaction value from the second to last pass differed by more than 2% from the average value in the last pass.